In the current printing industry, transition to aqueous ink systems (or water/low-volatile water-soluble organic solvent mixture-based ink systems) is in progress due to environmental concerns and other considerations. Since the aqueous systems are slow drying, their production speed is lower than the solvent systems. The aqueous system must be tailored so as to comply with high-speed operation targeting productivity improvements. It is required to improve the performance of ink so as to be compliant with high-speed printing and high-speed application.
Under such circumstances, in the ink and aqueous coating industries, there is a need for surfactants having a surface tension reducing ability and imparting a low contact angle so that the ink or coating composition may be improved in substrate wetting, substrate penetration and dispersion. For a choice of surfactant, a static surface tension is important when the system is stationary, whereas an index of dynamic surface tension is important during high-speed operation to meet a need for printing speed-up for the productivity improvement purpose.
Typical of known silicone-based surfactants are modified polysiloxane compounds. Among these, polyether-modified silicones are heretofore regarded useful as wetting and dispersing agents for ink and coating compositions, as described in Patent Documents 1 to 4. Patent Document 5 and 6 disclose ink compositions comprising dual end polyether-modified silicones. However, when added to ink compositions, not all polyether-modified silicones having excellent wettability and penetrability are effective for preventing color bleeding and providing good color development and printed image uniformity. It is difficult to identify the structure of polyether-modified silicones and select a proper one.
Patent Document 7 discloses an ink composition comprising different polyether-modified silicones. When this ink composition is printed onto relatively poor absorptive papers such as coated paper, problems like uneven printing, blur or bleeding arise. For the effect derived from such a combination of polyether-modified silicones, there is still left room to improve.